Pavement



March 26, 1929. J, F, DRISCOLL 1,707,055

PAVEMENT y Filed Jan. 2, 1925 Patented lV'Iar. 26, 1929. l

UNITEDv STATES JAMES FRANCIS DRISCOLL, OF BUFFALO, NEW YORK.

PAVEMENT.

Application filed January 2, 1925. Serial No. 45.

This invention relates to a pavement of the kind containing bitumen and commonly known as an asphalt or bituminous pavement, and has for its object the construction of a pavement of this character which has better wearing qualities and can be constructed more economically, owing to the reduced cost ot' equipment, the necessity for less skilled labor and the reasonable price of the materials which are required.

Heretofore pavements of this type usually have been constructed with a soft bitumen as a binding agent, or were constructed so as to carry a high bitumen content, and were regai-ded as more durable than one made ot' harder bitumen, or one having a lower bitumen content. They also have consisted o't simply a wearing course, consisting of tine materials such as sand, clay and dust, and the whole cemented together with bitumen. This wearing course was laid in one layer directly on the foundation of macadam or concrete, withoutthe employment of a binder course ot coarser materials between said wearing course and said foundation; or, a binder course of coarse materials bound together with bitumen has been used between said wearing course and said foundation, the object being to give stability to the wearing course and prevent shoving or waving under trafiic. While both ot these types served their purpose fairly well under slow-moving horse traffic, they have both been found absolutely unsatisfactory under fast-moving automobile and auto truck traic which pavements are required to carry at the present time, and which is getting heavier from year to year.

Other types of bituminous pavements have been constructed of crushed rock of various sizes.y some ot said rock being used just as it comes from the Crusher; some bt it with the fine particles first removed, and some of it with the addition of various quantities of sand, clay or dust, and the whole mass cemented together with bitumen. Generally a light or heavy wearing course has been added to receive the impact from traiiic. This type has failed because the moisture, which is ever present between a bituminous surface and the foundation, whether of macadam or concrete, but more so in macadam, has never been prevented rom entering the bottom of the wearing/course. The result has been disintegration starting at the bottom and working up through the pavement and causing the pavement to wave or shove and eventually fail entirely. This same trouble also applies to a wearing surface laid on abinder course, the large proportion of which is always coarse material.

That the asphalt and other types of bituminous pavements, as being laid at present, are not giving satisfactory service under present day conditions is shown by ,the fact that an investigation has recently been undertaken to see if there isnt some way of preventing shoves, or waves, in this type of pavements. These shoves not only render a pavement rough and unsafe to drive over, but soon destroy same.

The accompanying drawing is a fragmentary cross section of`a pavement constructed in accordance with my invention.

The pavement shownin this figure comprises a foundation 1 provided along each oi. its longitudinal sides or edges with a curb 2, a` lower layer of stratum 3 overlying the foundation, an intermediate layer or stratum 4 overlying the lower layer and forming with the latter the body course of the pavement, and an upper sealing coat, stratum or layer 5 overlying the intermediate layer.

Although the body course may be made up of various kinds and proportions of materials it has been vfound satisfactory by actual experience to employ a bituminous or composite paving mixture consisting of approximately of coarse rock or other suitable metal or mineral aggregate, graded from a size which will pass a screen having openings 1% inches in diameter down to a size which will be retained on a screen having openings 1A inch square, and approximately 40% of tine grit material or mineral aggregate properly graded from impalpable powder or dust, to a size which will pass a screen having 3 meshes to the lineal inch, all of which is cemented together with approximately 6% of bitumen or other suitable cementin;lr agent, and when properly manipulated will produce a body for a composite wearing surface of superior durability.

All of the materials mentioned are heated to a temperature so they can be thoroughly mixed by mechanical means until all the par` tieles are thoroughly coated with the cementing agent. The resulting mixture is taken to the street and spread over the foundation while still hot. In order to spread this mixt-ure to the proper grade and depth, this is done with hot rakes in such a way as to bring approximately all of the larger particles of CIJ Cil

rock or other metals away from the bottom of the mixture anddistrihute same throughout said mixture, with a considerable percentage of said la/rge particles on the surface of said body mixture, these large particles being brou ht to the surface in the same way that I face while raking a garden plot, at the same time leaving a large percentage of said tine materials at the bottom, which form a matrix that acts as a water-proof bottom seal coat. This matrix being hot and soft, as soonas laid, conforms to the irregular surface of the pavement foundation, regardless of whether the same is made of concrete or macadam, and acts as a keying agent, thereby assisting in preventing any shoving or waving of the surface of the pavement. .lhisraking yof the mixture containing the large lumps and rocks and other large particles of mineral aggregate is much more vigorous and continued for a longer period than ordinarily practiced for levelling or evening the surface of a mass or mixture, and in actual practice such raking is continued for a period of about three times the length of time required for merely levelling the mass, for the purpose of raising the large particles of mineral aggregate away from the bottom of the mass and thereby form a lower layer of mixture next to the foundation which is practically free from large rocks or mineral aggregate. While this body mixture is still hot I lightly roll same for the purpose of turning over the rough or sharp edges of any rock on the surface and to partly imbed said rock into said body mixture so as to leave a practically uniform and even surface on which to lay the wearing or seal coat. This raking or combing operation is done in such a way as to provide a perfectly sealed bottom of the body mixture practically free from large lumps or rocks on the underside, thereby making it iinpervious to any moisture which may penetrate the foundation and try to work its way through the bituminous pavement. It also distributes the rock throughout the mixture in such a Way as to key the finer particles in position and thereby prevent any tendency for said finer particles to roll, one on the other and form waves.

As soon as the light rolling above mentioned has progressed a short distance (say 1/2 wagon load) and while the body mixture is still hot, a seal coat or wearing surface, composed of the same line materialsas used with the rock in the body, as explained above, and containing approximately 10% of bitumen is laid direct-ly upon the newly rolled section of body course. This seal coat is also hot, and as soon as it is raked to the proper thickness it is immediately rolled with heavy rollers or umps and rocks are brought to the sur-l other means of compression whereby an absolute weld is obtained between the several layers, one course being pressed into the other. The result is a pavement having a tightly sealed bottom next to the supportlng foundation, with graded rock throughout the mixture or pavement and not under it as has been the custom heretofore; and having a tightly sealed upper surface which is impervious to moisture and is keyed into position and prevented from shoving by being welded while hot to the body course; also a surface which is uniform in thickness on account of the projecting lumps and rocks on the top of the body course being rolled enough to flatten same out without applying any considerable pressure to the body course until the two courses are finally rolled together with a heav machine, preferably 12 to 15 tons in weig t.

In a pavement laid in accordance with the foregoing method the several layers are welded together into one common mass in which no lines of division or separation are present between adjacent layers, which materially strengthens the pavement and prevents shoving or waving of the Same under the pressure ot the load passing over the same.

I claim as my invention The hereindcscribed method of constructing pavements which consists in laying on the foundation a mixture of bitumen, fine mineral aggregate and coarse mineral aggregate while this mixture is hot; raking said mixture while still hot and raising the coarse mineral aggregate therein from the lower part of the mixture to the upper part thereof and forming a lower layer of bitumen and fine mineral aggregate and an intermediate layer, above the lower layer, of bitumen, line mineral aggregate, and coarse mineral aggregate; light rolling these layers while hot so as to moderately compact the saine and turn over points of the coarse aggregate which may project upwardly after being laid on the foundation and cause the coarse aggregate to face upwardly with its wide surfaces; applying an upper finishing layer of bitumen and tine mineral aggregate while hot over Said intermediate layer while the lower and intermediate layers are hot; and then subjecting the lower, intermediate and upper layers while still hot, to a heavy rolling so as to compact the same and weld these layers together into one integral mass in which no line of division is present between the several la vers and the upper and lower Surfaces of the pavement are sealed against the entrance of water.

In testimony whereof I afiix my signature.

JAMES FRANCIS DRISCOLL. 

